1. Field of the Invention
The present invention relates to a filter array having a plurality of capacitance elements. More specifically, the present invention relates to a novel filter array having a plurality of capacitance elements, in which a plurality of 3-terminal capacitors are formed on a single dielectric unit such that the filter array can be utilized as a noise filter, for example.
2. Description of the Prior Art
One example of a conventional 3-terminal capacitor which is in the a background of the present invention and is utilized for a noise filter is shown in FIG. 1A and FIG. 1B. The conventional 3-terminal capacitor 1 as shown includes a dielectric unit 2, and electrodes 3a and 3b are formed on both main surfaces, respectively. Input and output terminals 4a1 and 4a2 are fixed to one electrode 3a, and a common terminal 4b is fixed to the other electrode 3b. Therefore, as shown in FIG. 1B, a capacitance C is formed between the input and output terminals 4a1 and 4a2 and the common terminal 4b. The input and output terminals 4a1 and 4a2 are inserted and connected to a signal line and the common terminal 4b is connected to ground.
Since the 3-terminal capacitor 1 has a self-resonance frequency higher than that of a conventional 2-terminal capacitor, the 3-terminal capacitor 1 can effectively exhibit a noise eliminating effect up to high-frequency region.
Another example of the conventional 3-terminal capacitor is shown in FIG. 2A and FIG. 2B. The 3-terminal capacitor 1 shown has a similar configuration to that of the 3-terminal capacitor as shown in FIG. 1A and FIG. 1B, but bead cores 5 are put on the input and output terminals 4a1 and 4a2, respectively. Therefore, in this example, as shown in FIG. 2B, in addition to the capacitance C, an inductance L is formed by means of cooperation of the input and output terminals 4a1 and 4a2 and bead cores 5, whereby a filter characteristic can be increased.
In the conventional 3-terminal capacitor 1 as shown in FIG. 1A and FIG. 1B or FIG. 2A and FIG. 2B, it is necessary to insert one 3-terminal capacitor for each signal line. Therefore, in case where such a 3-terminal capacitor is to be connected to each of a number of signal lines, a number of 3-terminal capacitors become necessary. Therefore, not only it is troublesome to mount such a number of 3-terminal capacitors on a circuit board but also the number of processing steps and a cost thereof increase.